In the development of current headlight systems, the foremost wish is increasingly to be able to project a light image having the highest possible resolution onto the roadway, light image which can be changed quickly and adapted to the respective traffic, road and light conditions. The term “roadway” is used here to simplify the description since, obviously, it depends on the local circumstances whether a light image is in fact on the roadway or extends beyond it. In principle, the light image is described based on a projection onto a vertical surface in compliance with the applicable regulations applying to passenger car lighting technology.
In order to satisfy this mentioned requirement, headlights have been developed, among others, in which a variably actuatable reflector surface is formed from a plurality of micromirrors and reflects a light emission generated by a light source in the emission direction of the headlight. Such lighting devices are advantageous in vehicle manufacture because of their highly flexible lighting functions, since the illumination intensity can be regulated individually for different light areas, and any desired lighting functions with different light distributions can be implemented such as, for example, a low-beam light distribution, a cornering-light light distribution, a city-light light distribution, a highway-light light distribution, a bending-light light distribution, a high-beam light distribution, or the formation of a glare-free high-beam.
For the micromirror arrangement, the so-called Digital Light Processing (DLP®) projection technology is used, in which images are generated in that a digital image is modulated onto a light beam. In the process, a rectangular arrangement of movable micromirrors, also referred to as pixels, which breaks up the light beam into sections and subsequently reflects it outward pixelwise into the projection path or out of the projection path.
The basis for this technology is formed by an electronic component which contains the rectangular arrangement in the form of a matrix of mirrors and their control technology and which is referred to as “Digital Micromirror Device” (DMD).
A DMD microsystem is a spatial light modulator (SLM) which consists of micromirror actuators, that is to say tiltable mirror surfaces arranged in the form of a matrix, having, for example, an edge length of approximately 16 μm. The mirror surfaces are constructed in such a way that they are movable due to the action of electrostatic fields. The angle of each micromirror is individually adjustable and each micromirror as a rule has two stable end states, between which it is possible to switch up to 5000 times within one second. The individual micromirrors can be actuated, for example, in each case by pulse width modulation (PWM) in order to represent, in the principal beam direction of the DMD arrangement, additional states of the micromirrors, whose time-averaged reflectivity lies between the two stable states of the DMD. The number of mirrors corresponds to the resolution of the projected image, wherein a mirror can represent one or more pixels. In the meantime, DMD chips with high resolutions in the megapixel range have become available. The technology underlying the adjustable individual mirrors is the micro-electro-mechanical-systems (MEMS) technology.
While the DMD technology has two stable mirror states, and the reflection factor can be set by modulation between the two stable states, the Analog Micromirror Device (AMD) technology has the property that the individual mirrors can be set in variable mirror positions which are in each case in a stable state there.
In the case of such vehicle headlights which can project several different high-resolution light distributions onto the roadway in front of the vehicle, there is a significant memory requirement. Control devices for micromirror arrangements are often implemented as an “embedded system.” Often such embedded systems are adapted specifically to a task and, for cost reasons, an optimized mixed hardware-software implementation is chosen. Therefore, in practice, the computing power and the available memory are often limited. It is often a disadvantage to use an additional external memory, since not only does the memory generate costs, but also the complexity of the “embedded system” is significantly increased, or respectively is not available commercially in the certification required for automobile applications.